Does your case have a removable cover? One that runs in a sliding slots on both sides? Is the extruded aluminum anodized?
If so, then it is approximately worthless for RF shielding. Aluminum anodizing is an insulator. Which means that the cover is not well grounded to the rest of the case. Research "slot antennas." A slot in a plane of metal is just as good a radiator as a metal dipole in open space. What is the resonant frequency of the metal box when viewed as a resonant cavity? It will actually increase the radiated spurs of the basic product (the BBB and anything else with clocks) at the resonant frequency(s) of the case. As an experiment, drive some metal screws into the junction between the case and the cover, to get better grounding. Grind the anodizing off the case at any point that you need a metallic ground to the aluminum case. If you are using the slots inside the case to hold circuit cards, don't assume that you are getting any grounding through the slotted ridges, because they are anodized. As Gerald suggests, get some clamp-on ferrites or ferrite beads (appropriate for the frequency range of concern) and start putting them on every cable entering or exiting the case. Use shielded cables, and ground the shields at the point of exit/entry. Good luck. --- Graham == On Monday, July 25, 2016 at 7:09:03 AM UTC-5, Gerald wrote: > > When doing this, you need a good power supply with a choke on it and a > good Ethernet cable, one that is shielded costs more money than your > typical cable. I have no idea what your cape is doing, Having it in a case > can help, but the real issues are related to the cables that come into and > out of the enclosure. > > Gerald > > On Mon, Jul 25, 2016 at 7:03 AM, David Accadia <[email protected] > <javascript:>> wrote: > >> >> We are planning to use the Beagle Bone black in a commercial product, We >> have designed a custom cape and put the whole thing inside an aluminum >> housing. The system has been sent off for EMC testing but unfortunately >> the testing lab has failed conducted emission. There where a lot of peeks >> but the following frequencies failed >> >> >> 180MHz >> 203MHz >> 228MHz >> 250MHz >> 288MHz >> 312MHz >> 372MHz >> 384MHz >> 396MHz >> 420Mhz >> 468MHz >> 480MHz >> 875MHz >> 1000MHz >> >> To try and isolate the issues we've acquired a spectrum analyzer and a >> set of near field probes. From my testing with the near field probes It >> seems that most of the failed frequencies are coming from the beagle bone >> black. >> >> I've noticed the 1000MHz and 250MHz peeks (which where the biggest) >> seemed to go when the Ethernet cable was is removed. Many of the other >> peeks seemed to match up with the peeks on the beagle bone black FCC >> report. ( >> http://elinux.org/Beagleboard:BeagleBoneBlack#Regulatory_Compliance_Documents) >> >> The once that don't also seem to go when the beagle bone is powered off. >> The system sits inside an extruded aluminum housing and the end plates >> are actually PCBs with single plane of copper. So there is lot I can still >> do to tighten up the enclosure. Although based on the report I would have >> expected the BBB to pass outside an enclosure. >> >> >> Has any one else had similar experience with the beagle bone black and >> EMC problems? And how did you solve them? >> >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/beagleboard/5a62f4ad-5745-4814-8f2c-08ad0a665d71%40googlegroups.com >> >> <https://groups.google.com/d/msgid/beagleboard/5a62f4ad-5745-4814-8f2c-08ad0a665d71%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > Gerald > > [email protected] <javascript:> > http://beagleboard.org/ > [email protected] <javascript:> > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/67567e99-6f00-49a0-9017-33ddb302305a%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
